SAN DIEGO -- Portions of San Diego County will be under a heat advisory for a fourth consecutive day Friday as a late-summer heat wave continues to drive temperatures in some areas well into the triple digits.

On Thursday, a high temperature of 96 degrees in the city of San Diego was one degree higher than the previous record for a Sept. 10, set in 1878. A 94-degree high in Chula Vista topped by four degrees a prior record for the day, set in 1990. Minimum temperatures in several areas also tied or broke records.

Early Friday, warm weather and punishing humidity were already prevalent in some areas.

"It is another warm morning across Southern California unless you are fortunate enough to be in the mountains where temperatures are in the 50s and 60s,” according to the National Weather Service. "Elsewhere temperatures at 2 a.m. were in the mid-70s to low 80s, with a few of the inland valleys dipping into the low 70s."

A heat advisory for the coast and the valleys is scheduled to expire at 6 p.m.

"High pressure aloft will continue hot daytime weather today," according to the weather service. "Temperatures will be 5 to 10 degrees above normal."

Highs of 82 to 87 degrees are forecast today for the coast, 87 to 92 degrees in inland areas, 89 to 94 in the valleys, 84 to 92 in the mountains and 98 to 103 degrees in the deserts.

A slight chance of afternoon and early evening thunderstorms stemming from monsoonal moisture is also in the forecast. The weather service pegged the chance at measurable precipitation at 20 percent in the valleys and deserts, and at 40 percent for the mountains.

Forecasters again urged people to protect themselves and their loved ones against dehydration, heat stroke and other heat-related illnesses. Residents were advised to stay well-hydrated, avoid working in the sun, check on neighbors and relatives -- especially the elderly -- and provide plenty of water to pets and livestock.

Authorities also warned against leaving children or pets in parked cars, which can rapidly become death traps in high heat.

Cooler weather is expected to kick in over the weekend and continue into next week, forecasters said.